1. Field of the Invention
The present invention relates to sheet stretching devices and particularly to graphic arts paper stretching devices wherein the paper is watercolor paper.
2. Description of the Related Art
One problem encountered when painting a watercolor is when wet washes are applied to the watercolor paper, the paper expands in the wetted areas only, and as a result the paper buckles. When the paper dries the buckling does not disappear; in fact, the buckling becomes semi-permanent and can only be removed with special techniques. The buckles, in turn, result in depressions in the paper. The ridges and depressions in the paper make it difficult to control the behavior of subsequent washes. Tinted washes tend to flow away from the ridges towards the depressions causing the intensity of colors to vary in a way the artist did not intend.
When a buckled painting is finished and ready for framing, the paper must be flattened first by dampening the entire sheet and letting it dry under a flat surface such as a wooden board.
The buckling phenomenon described above occurs more noticeably with thinner papers of 140 lb and thinner. Thicker watercolor papers of 300 lb and higher do not buckle as much and are quite manageable. However, thicker papers cost more than thinner sheets thus limiting some artists in their choice of paper thickness.
The solution to buckling used by most watercolor painters is to stretch the paper on a suitable board prior to painting. The way this is normally done is to soak the entire sheet of watercolor paper with water for about five to ten minutes and allowing the paper to expand. Then the wet paper is attached to a flat board along its edges, either with staples or wetted gummed tape and left to dry for several hours or overnight. While drying, the paper contracts and becomes taught and flat on the board. Stretching the paper as described above makes the paper much less prone to buckling. Even when heavily wet washes are applied to the stretched paper, and some buckling does occur, the paper will re-assume its taught and flat condition when dry.
The process of stretching watercolor paper is time consuming and troublesome in a number of ways. For example, sometimes the gummed tape used to stretch the paper gives way to the tension applied to it by the paper and the paper has to be re-stretched. Also, removing the tape when the painting is finished may at times damage the paper in spots or leave tape residue. When using staples, some staples do not penetrate the board as intended, and must be removed and reapplied. Removing the staples after the painting is done is also time consuming. And, of course, the most time-consuming aspect of stretching watercolor paper is the time waiting for the paper to dry. Some artists overcome the problem of drying time by preparing several stretched sheets ahead of time.
To ease the problems of watercolor paper stretching several inventions have appeared. However, most of those inventions address only the problem of attaching a wetted sheet of watercolor paper to a board, and have successfully eliminated the need for gummed tape and staples for this purpose. Examples of these devices are shown in U.S. pat. No. 4,126,952, 4,277,901, and 4,862,610. These inventions, however, do not solve the problem relating to the time involved with waiting for the watercolor paper to dry in order to become taught.
Closely related to watercolor paper stretchers are canvas stretchers for oil and acrylic painting. Numerous inventions exist addressing the problem of stretching canvas on a frame. Some of these inventions could be modified to be applicable to watercolor sheets. It should be noted here that the requirements for preparing canvas for oil or acrylic painting are somewhat different from those required for preparing watercolor sheet. Oil and acrylic painters do not need a solid backing for their canvases. Most oil painters have their canvases stretched onto an open frame with no backing under the canvas. Watercolor painters, however, require a solid backing for their papers for several reasons. First, since paper will expand when wetted, paper on an open frame will tend to sag when wet washes are applied. Furthermore, watercolor painting often involves techniques such as "Lifting" and "Scratching" that require a solid backing because these operations apply significant force onto the paper surface. Therefore, frame stretchers are not quite applicable to watercolor paper stretching. Never-the-less, a discussion of frame stretchers is presented below since some of the concepts involved in frame stretchers could, perhaps, be applied to stretching watercolor paper.
One problem with many frame stretchers is that most of them stretch the canvas along two perpendicular axes by simply increasing the distance between opposing frame members. And, if the canvas is attached, for example, with staples, all along the frame members, then the canvas is restricted from stretching along the frame members because the frame members themselves do not expand. Examples of such canvas stretchers are disclosed in U.S. Pat. Nos. 4,301,853, 4,565,020 and 5,918,392. One patent that recognizes the above problem is U.S. Pat. No. 4,144660. In this patent the inventor has provided means for increasing the length of each frame member after the canvas has been attached to the frame. The inventor has done this by having each frame member consist of several segments, and providing means for increasing the space between each of the segments, thereby increasing the overall length of each frame member. U.S. Pat. No. 5,115,584 has also solved the problem of restricting the canvas from stretching along the frame members. In this patent the canvas is not attached to the frames at all. The canvas is stretched using resilient clips to stretch the canvas over the frames, but the canvas is free to stretch along the frame members. The latter two cited inventions, however, are not suitable for stretching watercolor paper since they do not provide a solid backing under the stretched sheet, something that the watercolor paper should have as explained above.
It is evident from the above that it would be highly beneficial for watercolor artists if they had a device that could stretch watercolor paper in its dry state within a matter of minutes, never having to wet it prior to stretching, nor wait for hours for the paper to dry. Furthermore, what is needed by watercolor artists is a paper stretching device that provides a solid backing under the watercolor paper. Another improvement that would benefit watercolor artists is the reduction in the time consumed by attaching and detaching watercolor paper from a board.